Here is the full list of all 119 Torchlight II achievements. It takes around 200 hours to unlock all of the achievements on Windows.
Sell 50,000 items
Use 100 maps
Destroy 100 socketed gems
Socket 500 gems into items
Defeat the Nether King with each of the 4 classes
Defeat the Nether King in hardcore mode (casual)
Defeat the Nether King in hardcore mode (elite)
Defeat the Nether King in hardcore mode (normal)
Defeat the Nether King in hardcore mode (veteran)
Defeat the Nether King as an Outlander
Fish 1,000 times
Find 100 secret rooms
Defeat the Nether King as an Embermage
Deal 100,000 critical strikes
Defeat the Nether King as a Berserker
Have 50 friends
Recover 100 gems from items
Use 5,000 potions
Break 10,000 breakables
Destroy 10 socketed gems
Sell 5,000 items
Squish 1000 critters
Use 10 maps
Defeat 500 champions
Find a legendary item
Have 10 friends
Socket 50 gems into items
Explode 10,000 enemies
Find 10 secret rooms
Recover 10 gems from items
Defeat the Wraith Lord
Wear a completed armor set
Obtain a tier 3 skill bonus
Reach level 100
Squish 500 critters
Take 100,000 steps
Deal 10,000 critical strikes
Use an enchanter 500 times
Break 1,000 breakables
Begin new game plus
Use a map
Defeat Aleera
Defeat Verona
Defeat Marishka
Defeat the Nether King in Casual difficulty
Defeat the Nether King in Elite difficulty
Defeat the Nether King in Normal difficulty
Defeat the Nether King in Veteran difficulty
Defeat the Nether King as an Engineer
Defeat the Nether King
Defeat the Dark Alchemist
Assemble TrillBot
Defeat Killbot
Defeat Vyrax
Defeat Thiss
Defeat Cacklespit
Defeat Bloatfang
Defeat the Grizzled Alpha
Obtain a tier 2 skill bonus
Open 500 chests
Defeat Boletus Rex
Purchase 100 items from the gambler
Defeat the Siege Guardian
Do 10,000 damage with a single attack
Defeat the King In Masks
Defeat Ezrek Khan
Defeat 100 champions
Defeat Aruk
Use an enchanter 50 times
Use an enchanter 10 times
Purchase 50 items from the gambler
Have 100,000 gold
Have 1,000,000 gold
Have 10,000,000 gold
Purchase 20 items from the gambler
Teach a pet 4 spells
Defeat the Artificer
Take 50,000 steps
Die with a hardcore character
Start a hardcore character
Squish 100 critters
Defeat the Manticore's Mate
Defeat the Manticore
Fish 100 times
Sell 500 items
Teach a pet a spell
Fish using dynamite
Recover a gem from an item
Destroy a socketed gem
Defeat Grand Regent Eldrayn
Learn 4 spells
Join a multiplayer game
Add a friend
Trade an item with another player
Start a multiplayer game
Explode 1,000 enemies
Defeat King Pogg
Deal 1,000 critical strikes
Defeat Chillhoof
Use 500 potions
Defeat Kidrik the Mauler
Defeat the Winter Widow
Open 100 chests
Defeat 25 champions
Defeat General Grell
Find a secret room
Take 10,000 steps
Learn a spell
Defeat Mordrox
Defeat One-Eyed Willy
Obtain a tier 1 skill bonus
Socket a gem into an item
Break 100 breakables
Explode 100 enemies
Defeat the Fallen Guardian
Use 50 potions
Open 20 chests
Send your pet to town
Fish 10 times